Method for fabricating a cathode ray tube

ABSTRACT

A method for fabricating a cathode ray tube is described. The method comprises the steps of selectively forming a resist layer corresponding to a pattern of a fluorescent material on an inner surface of the panel of a cathode ray tube, and applying a slurry of a light-absorbing material on the entire inner surface of the panel including the resist layer to form a light-absorbing layer. An inorganic pigment slurry is applied over the entire inner surface of the panel to form an inorganic pigment layer on the light-absorbing layer and then subjected to reverse development to selectively remove the resist layer along with the light-absorbing layer and the white pigment layer, thereby forming a matrix pattern. Finally, a fluorescent material is applied to individual removed portions of the matrix pattern to form a fluorescent pattern. Monochromatic or color cathode ray tubes are obtained with an improved luminance and a colorimetric purity by a simple procedure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for fabricating a cathode ray tubehaving a high degree of fineness and, more particularly, to an improvedmethod for obtaining a luminance and a colorimetric purity for a cathoderay tube panel.

2. Description of the Prior Art

In order to form images with a high fineness in cathode ray tubes, it isnecessary to form a fluorescent layer having a very fine pattern of adistinctly striped or dotted form on a panel surface without anyseparation. For accurate landing of an electron beam on such a finepattern, a beam spot has to be converged as small as possible. Tosupplement the shortage of the luminance, techniques of improving theluminance of the panel surface are essential.

In recent years, however, as the fineness of the panel surface isremarkably improved, it is becoming more difficult to deposit and keepfluorescent particles in an optimum amount in a desired position. Thisis because when the fluorescent layer containing fluorescent particlesis formed in a fine pattern, its adhesion to the panel surface islowered so that the fluorescent layer is liable to come off at the timeof development. Such coming off or removal will cause the color balanceto be lost and the luminance to be lowered. It may be considered that ifthe fluorescent layer is made thin, the layer is prevented from comingoff, but it has a lower luminance. Accordingly, there is a strong demandfor techniques of effectively preventing the fluorescent layer fromcoming off when the layer is formed with a relatively large thickness.However, no effective measure has yet been proposed.

On the other hand, several techniques have been proposed for improvingthe luminance of the panel surface irrespective of the prevention of thefluorescent layer from coming off or being removed.

One such typical example is a metal backing. This is a technique offorming an aluminum thin film having a high light reflectance and a highelectron transmittance on the fluorescent layer, for example, accordingto a vacuum deposition method. Among fluorescence rays which thefluorescent material emits by energization with an electron beam, thecomponent directed toward the back face is reflected in the forwarddirection to improve the brightness of the picture. Besides, the metalbacking has functions of preventing an ion spot and stabilizing thepotential of the fluorescent face.

In the metal backing step, prior to the vapor deposition of the aluminumfilm, a thermally decomposable intermediate film, such as of nitrocellulose, polymethacrylate, acrylic emulsions or the like, is smoothlyformed. This intermediate film is removed by decomposition during asubsequent thermal treatment, leaving an aluminum film alone on theinner surface of the panel. In order to improve the luminance of thecathode ray tube, it is essential; to form the aluminum thin film in astate of a mirror surface. To this end, the intermediate layer is formedwith a relatively large thickness to absorb the surface irregularitieson the fluorescent layer. Alternatively, for the formation of theintermediate film, the inner surface of the panel has water appliedthereto, after which a lacquer is developed thereon.

Another approach for improving the luminance of the panel surface is atechnique wherein a light reflection layer having a high lightreflectance is formed on the light-absorbing matrix, such as by a vacuumdeposition, an application of slurry or the like. The present inventiondefines a light-absorbing matrix as a pattern of a striped or dottedform on a panel surface.

For instance, Japanese Patent Publication No. 63-29374 discloses atechnique of depositing a nickel thin film by an electroless plating ofnickel-phosphorus selectively on a carbon matrix. In a cathode ray tubeOf the type where a fluorescent layer is formed to extend onto thecarbon matrix according to a so-called inside exposure method, thenickel thin film can prevent light emitted from the fluorescentparticles from being absorbed in the carbon matrix, thereby improvingthe luminance and the contrast ratio on the panel surface.

Further, similar results are obtained by a technique disclosed inJapanese Patent Publication No. 63-40011, wherein a suspensioncontaining both a light-absorbing material, such as graphite, and alight diffusion and reflection material, such as titanium oxide, isapplied on the inner surface of the panel and developed to form a lightdiffusion and reflection layer on the carbon matrix.

3. Problems to be Solved by the Invention

However, in the prior art techniques, many problems are left to besolved.

First, although the prior techniques show effects to an extent withrespect to the improvement in the luminance, the coming-off problem ofthe fluorescent layer is not solved by any existing technique. Moreparticularly, the light reflection layer formed by plating, vacuumdepositing or applying slurries has so smooth a surface that highadhesion to the fluorescent layer cannot be expected. In addition, thetechnique of forming the light reflection layer by electrolessnickel-phosphorus plating is complicated in the formation step.

Second, the improvement of the luminance by the prior art techniques islimited and, especially, the problem of the lowering of the colorimetricpurity in the color cathode ray tube has not been solved. This is aproblem having a relation to the formation of the fluorescent layer.

The formation of the fluorescent layer can be broadly classified into aninside exposure method wherein light is exposed from the side of theinner surface of the panel and an outside exposure method wherein lightis exposed from the outer side of the panel as proposed by the sameapplicants in Japanese Laid-Open Patent Application No. 60-119055.

In general, in the inside exposure method, the light exposure forforming the fluorescent layer is performed from the inside of the innersurface of a panel glass, so that, as shown in FIG. 5, part of afluorescent layer 25 is partially extended over a carbon matrix 22.Accordingly, there is, for example, a luminous ray component which isemitted from the fluorescent particles and is directly absorbed in thecarbon matrix 22, as shown by arrow l₁₁ in FIG. 5, or another luminousray component, as shown by arrow l₁₂, which is reflected from a metalbacking film 26 and is then absorbed in the carbon matrix 22. Thus,there exists a problem that the luminance is not improved even thoughthe amount of the fluorescent particles is large.

According to the technique of the Japanese Patent Publication No.63-29374, the lowering of the luminance can be suppressed to an extentwhen a thin nickel film is deposited on the carbon matrix. However,since the fluorescent layers are formed by the inside exposure methodand the distance between adjacent fluorescent layers becomes small, aluminous ray emitted from a given fluorescent particle passesstraightly, as shown by an arrow l₁₃, in FIG. 5 or is reflected by themetal backing film 26, as shown by arrow l₁₄, with the possibility ofentering an adjacent fluorescent layer 25'. With color cathode raytubes, adjacent fluorescent layers 25, 25' contain fluorescent particlesof different colors from each other and, thus, the passing of raysbetween the layers 25 and 25' will cause the colorimetric purity to belowered. The thin nickel film does not have such a height as toestablish a partition wall between the fluorescent layers 25, 25', sothat luminous rays, as shown by the arrows l₁₃ and l₁₄ cannot beeffectively shielded or stopped.

To cope with the problem of the color mixing, there has been proposed adeposition of a thin nickel film only on marginal portions of the carbonmatrix 22. In this arrangement, a light-absorbing effect at the centralportion of the carbon matrix 22 is expected with the luminance-improvingeffect being reduced.

The outside exposure method is a technique of enabling one to formself-aligned fluorescent layers through a carbon matrix mask by exposinglight from the outside of the panel. According to the outside exposuremethod, the fluorescent layer 24 is not extended over the carbon matrix22, as shown in FIG. 4, but is selectively formed on non-formed portionor window portions of the carbon matrix 22. Thus, the uniformity andcolorimetric purity can be remarkably improved when this method isapplied to color cathode ray tubes.

However, the loss of the luminance cannot be avoided even with the useof the outside exposure method for the following reason. In the outsideexposure method, sharp steps are formed between the regions where thethick fluorescent layer 24 has been formed and the regions where thethin carbon matrix 22 has been formed. If, for example, an acrylicemulsion is used to form an intermediate layer (not shown), the emulsionis liable to flow toward a recess (i.e. the carbon matrix). Theresultant intermediate film is formed with an incline, which isinevitably provided on a metal backing layer 26 formed thereon.Accordingly, among luminous rays emitted from fluorescent particles,there is a component which is reflected at the inclined face 26a of themetal backing film 26, as shown by arrow l₁₀, and this reflectedcomponent is finally absorbed in the carbon matrix 22 to lead to a lossof the luminance.

The common problem involved in the inside exposure method and theoutside exposure method is that a so-called aluminum lifting, i.e., theseparation of the metal backing, takes place. This is because, as statedabove, the intermediate film is liable to be formed as a thick portionon the carbon matrix and an amount of the gases generated from the thickportion during the thermal decomposition step becomes so large that anadditional pressure of the gases is exerted on the metal backing film.The separation results in a lowering of the luminance. In order to avoidthe partial difference in the thickness of the intermediate film, theintermediate film may be formed entirely as a thick film. This willcontribute to an increase in the degree of the mirror surface of themetal backing film, but will also increase an amount of the gases fromthe decomposition and unfavorably facilitate the aluminum lifting.

Thus, it is very difficult in the prior techniques to simultaneouslyachieve the prevention of both the fluorescent layer from coming off andthe aluminum lifting and the improvements in the luminance and thecolorimetric purity.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a method forfabricating a cathode ray tube which can solve the problems involved inthe prior art techniques.

It is another object of the invention to provide a method forfabricating a cathode ray tube with an improved luminance of the cathoderay tube wherein an inorganic pigment layer having relatively greatirregularities is formed selectively on a light-absorbing matrix on aninner surface of a panel of the cathode ray tube and serves as a kind ofpartition wall for adjacent fluorescent layers whereby the fluorescentlayers are prevented from coming off and the metal backing film isprevented from separation.

It is a further object of the invention to provide a method forfabricating a color cathode ray tube which has an improved colorimetricpurity.

We have made intensive studies in order to achieve the above objectsand, as a result, found that when partition walls, which have relativelylarge irregularities on the surface, are formed on a light-absorbingmatrix, it becomes possible (1) to prevent fluorescent layer from comingoff due to higher adhesion to the fluorescent layer, (2) to improve thecolorimetric purity by physically limiting the region where thefluorescent layer has been formed, (3) to make uniform the steps on theinner surface of the panel and to prevent aluminum lifting owing to thisuniformity, and (4) to form pinholes in the metal backing by the actionof the surface irregularities to prevent the aluminum lifting.

If white inorganic pigment powders having a high light reflectance areused to form the partition walls, luminous components which are absorbedin the light-absorbing matrix in the prior art can be effectivelyutilized in addition to the above effects. In addition, when theinorganic pigment powder has a very small size, the fabrication stepbecomes very simple.

According to the present invention, there is provided a method forfabricating a cathode ray tube of the type which includes a panel havinga fluorescent pattern on an inner surface of the panel. The methodcomprises the steps of:

selectively forming a resist layer corresponding to a fluorescentpattern on an inner surface of a panel of a cathode ray tube;

applying a slurry of light-absorbing material on the entire innersurface of the panel including the resist layer to form alight-absorbing layer;

applying an inorganic pigment slurry dispersing an inorganic pigmentpowder therein over the entire inner surface of the panel to form aninorganic pigment layer;

selectively removing the resist layer, the light-absorbing layer and thewhite pigment layer provided on the resist layer by a reversedevelopment to form a matrix pattern; and

forming a fluorescent layer at least on the respective removed portionsof the matrix pattern.

Preferably, the inorganic pigment slurry is applied by spraying it overthe entire inner surface. For this purpose, the inorganic pigment powderused in the slurry should preferably have a size of not larger than 1μm.

The removed portions of the matrix pattern where the fluorescent layeris to be formed may be called window portions of the matrix. Iffluorescent layers of the three primaries or origin colors are,respectively, applied to the removed portions so that the threeprimaries are arranged side-by-side in the fluorescent pattern, a colorcathode ray tube can be fabricated.

Other advantages and features of the invention will be readily apparentfrom the following description of the preferred embodiments, thedrawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are, respectively, schematic cross sectional views of partof a cathode ray tube fabricated according to the invention wherein FIG.1 shows a case where a fluorescent layer is formed according to anoutside exposure method and FIG. 2 shows a case using an inside exposuremethod;

FIGS. 3(A) to 3(F) are, respectively, schematic cross sectional viewsshowing a procedure of fabricating a color cathode ray tube of thestripe type in the order of steps wherein FIGS. 3(A) shows the step offorming a resist layer and a carbon layer, FIG. 3(B) shows the step offorming a white pigment layer, FIG. 3(C) shows the step of forming amatrix pattern according to a reverse development, FIG. 3(D) shows thestep of forming fluorescent stripes of the three primary colors, FIG.3(E) shows the step of forming an intermediate film and a metal backingfilm, and FIG. 3(F) shows the step of removing the intermediate film bydecomposition through thermal treatment; and

FIGS. 4 and 5 are, respectively, schematic cross sectional viewsillustrating problems involved in known cathode ray tubes wherein FIG. 4shows a case where a fluorescent layer is formed according to an outsideexposure method and FIG. 5 shows a case using an inside exposure method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The important aspect of the invention resides in a fact that alight-absorbing layer with a thickness of approximately 1 μm is formedby applying a carbon slurry on an entire surface of an inner surface ofa panel by a known method, and a slurry with an inorganic pigment powderdispersed therein is applied and, preferably, sprayed over the entiresurface to form an inorganic pigment layer.

The inorganic pigment powder should have thermal stability which isresistant to about 500° C. because the powder is heated to not lowerthan 400° C., for example in an electric furnace, in a subsequentthermal decomposition step of an intermediate film. Favorable examplesof the inorganic pigment material include C, MnO₂, CaO, TiO₂, Al₂ O₃,MgO, ZnS and the like. The materials except for the former two materialsare white in color and are preferred in those cases where theimprovement in the luminance is expected.

For preparing a slurry of the inorganic pigment powder, which isexcellent in handling properties, the size of the inorganic pigmentpowder should preferably be not larger than 1 μm. Care should be paid tothe size if commercial products having various particle sizes areavailable. For example, TiO₂ powders of the rutile type having a size of2-3 μm and TiO₂ powders of the anatase type having a size ofapproximately 0.1 μm are commercially sold. In the practice of theinvention, the latter powders are favorable.

The inorganic pigment slurry is prepared by mixing the inorganic pigmentpowder with colloidal silica, pure water and the like.

The colloidal silica is used as an adhesive between the inorganicpigment powder and the light-absorbing layer (usually a carbon matrix).With a commercial product having Si content of about 30%, the silica ispreferably used in an amount of 100 to 500 ml per 500 g of TiO₂. If theamount is less than the above range, good adhesion cannot be obtained.If the amount is over the above range, the adhesion force becomes greatbut a problem with the separation of the resist layer during the reversedevelopment will occur.

Pure water is a dispersion medium for the inorganic pigment slurry andis used in an amount of about 500 to 1000 ml per 500 g of TiO₂. Theamount of pure water influences the viscosity of the resultant inorganicpigment slurry and should be appropriately determined depending on theopening of a spray nozzle.

The inorganic pigment slurry is low in viscosity immediately after thepreparation under agitation and may undergo so-called thixotropy whereinthe viscosity increases with time when the slurry is allowed to stand.If necessary, dispersants, such as a surface-active agent, may be addedin an amount of 0.05 to 0.5 wt % based on the slurry.

In the thus prepared inorganic pigment slurry, coagulums are inevitablyformed and the size of the coagulums should preferably be about 20 μm orbelow for the reason stated hereinafter.

In the practice of the invention, formation of the inorganic pigmentlayer is effected without use of spin coating by spraying of theinorganic pigment slurry. This is because spraying is more advantageousin increasing the surface irregularities in the inorganic pigment layer.If the coagulums are selected to have a size of about 20 μm or below,the projections having a height of approximately 5 to 25 μm can beformed on the upper surface of the inorganic pigment layer. The drythickness of the inorganic pigment layer should preferably be in a rangeof about 10 to 20 μm, although it depends on the diameter of the dots orthe pitch of stripes of the matrix pattern (provided that the height ofthe projections is not included). This range is set from the standpointthat not only is the aspect ratio of the window portions of the matrixpattern made so great as to ensure the contact area with the inorganicpigment layer, but also the inorganic pigment layer will function as aphysical partition wall between adjacent fluorescent layers and toprovide a satisfactory reflectance when the inorganic pigment is whitein color.

It will be noted that the formation of the inorganic pigment layer doesnot influence either the reverse development, by which the resist layeris removed, or the steps of forming the fluorescent layer and the resistlayer.

The fabrication method of the invention comprises, after formation of alight-absorbing layer over an entire surface of an inner surface of apanel by application, for example of a carbon slurry, an additional stepof forming an inorganic pigment layer by spraying an inorganic pigmentslurry with an inorganic pigment powder dispersed therein. When aninorganic pigment powder having a size of not larger than 1 μm is used,a stable slurry having good handling properties can be prepared and theresulting inorganic pigment layer becomes clear at the edge portions.The inorganic pigment layer can pass water therethrough and does notpresent any trouble during a reverse development for removal of a resistlayer. In addition, the inorganic pigment layer does not influence thesteps of forming a fluorescent layer and an intermediate layer.Accordingly, this formation step can readily be incorporated in theexisting fabrication processes of cathode ray tubes.

Reference is now made to the accompanying drawings and particularly toFIGS. 1 and 2 wherein part of a panel of a cathode ray tube of thestripe type which is fabricated according to the invention isschematically shown. FIGS. 1 and 2, respectively, show formation of afluorescent layer according to an outside exposure method and an insideexposure method. In these Figures, like parts are indicated by likereference numerals.

The panels are those which are obtained by forming carbon stripes 2 withgiven pitches on a glass panel 1 and then an inorganic pigment layer 3,which has a thickness of 10 to 20 times greater than that of the carbonstripe 2, is formed on the stripes 2. A fluorescent layer 4 or 5 isformed on carbon stripe-free portions or window portions and then theentire surface is covered with a metal backing film 6.

The inorganic pigment layer 3 shows various effects in the practice ofthe invention.

The first effect is prevention of the fluorescent layer 4 or 5 fromcoming off. Since the inorganic pigment layer 3 has relatively largesurface irregularities, the fluorescent layer 4 or 5 formed in contactwith the inorganic pigment layer 3 can be strongly kept. Accordingly,thin film formation of the fluorescent layer, which thin film mayinvolve a lowering of the luminance, for the purpose of preventing thefluorescent layer from coming off as in prior art is unnecessary.

The second effect is prevention of the aluminum lifting. Part of theprojection 3a present in the surface of the inorganic pigment layer 3reaches the metal backing film 6 and passes therethrough to thereby formfine pinholes 6a. The pinholes 6a function as a kind of vent ports whenan intermediate layer (not shown) is removed by thermal decomposition,so that any lifting of the metal backing film 6 does not take place.This allows the formation of a thick intermediate film, along with theadvantage that the degree of mirror surface of the metal backing film 6can be increased.

The third effect is that, especially in color cathode ray tubes, thecolorimetric purity can be improved. The inorganic pigment layer 3contributes to an increase in the aspect ratio of the window portions.Since the thickness of the fluorescent layer 4 or 5 is the same as thatin prior art, the inorganic pigment layer 3 functions as a partitionwall for separating the fluorescent layers. More particularly, the.inorganic pigment layer 3 not only physically limits a region where thefluorescent layer 4 or 5 is formed and, especially, where thefluorescent layer is formed according to the inside exposure method, butalso inhibits a luminous component from entering adjacent fluorescentlayers. Thus, it is expected that the colorimetric purity is improved incolor cathode ray tubes.

If the inorganic pigment layer 3 is constituted of white inorganicpigments, the luminance can also be improved for the following reason.

With the fluorescent layer 4, which is formed according to the outsideexposure method as shown in FIG. 1, fluorescence l₁ emitted from afluorescent particle is reflected at the side wall of the inorganicpigment layer 3. In addition, fluorescence l₂, which would be absorbedin the light-absorbing matrix in the prior art, is reflected with ametal backing film 6 and then also reflected by an upper portion of theinorganic pigment layer 3. These components are returned to the interiorof the fluorescent layer 4.

Such an effect is similarly produced with the fluorescent layer 5, whichis formed by the inside exposure method, as shown in FIG. 2. Luminousrays l₃ and l₄ emitted from the fluorescent particles are similarlyreturned to the interior of the fluorescent layer 5. Thus, the effectiveutilization of the light emission of the fluorescent particles ispossible with an improved luminance of the panel.

With the color cathode ray tubes, the color mixing will be avoided, dueto the presence of the inorganic pigment layer 3, with an increasingallowance of beam landing.

A preferred embodiment of the invention which is applied to fabricationof a color cathode ray tube of the striped type according to an outsideexposure method using white TiO₂ as the inorganic pigment is moreparticularly described with reference to FIGS. 3(A) to 3(F).

The arrangement of a panel of the color cathode ray tube fabricatedaccording to this invention is similar to that shown in FIG. 1.

A photoresist aqueous solution, such as, for example, an aqueoussolution obtained by dissolving 8 wt % of ammonium bichromate based onpolyvinyl alcohol in 1.5% polyvinyl alcohol aqueous solution, was spincoated on an inner surface of a glass panel 11 and dried. Thereafter, UVexposure was effected three times using an aperture grill as an opticalmask in such a way that the position of an exposure light source wasshifted corresponding to positions of light sources for red, green andblue colors, followed by developing treatment to selectively form aresist layer 17 corresponding to a fluorescent pattern, as shown in FIG.3(A). Subsequently, a carbon slurry was applied over the entire innersurface of the panel 11 including the resist layer 17 and dried to forma carbon layer 12. The thickness of the carbon layer 12 is about 1 μm inportions where no resist layer 17 has been formed.

As shown in FIG. 3(B), an inorganic pigment slurry with an inorganicpigment powder dispersed therein was sprayed over the entire innersurface of the panel and dried to form an about 15 μm thick inorganicpigment layer 13. An example of a composition of the inorganic pigmentslurry used was composed of 350 g of TiO₂ powder (extra pure reagent,anatase, particle size 0.1 μm, available from Kanto Chem. Co., Ltd.),280 ml of colloidal silica (Si content of 30%, commercial name: RudoxAM, available from Du Pont de Nemours), 8 ml of an acrylic emulsion(acryl content of 10%, commercial name: Primal 850, Rhom & Haars Inc.)and 600 ml of pure water. A surface-active agent was added as adispersant so that a stable slurry having good handling properties couldbe prepared.

Either a hydrogen peroxide aqueous solution or a periodic acid aqueoussolution, which is used as a reverse developing agent for decomposingthe resist layer 17, was injected into the panel, followed by blowingwater to remove the resist layer 17 along with any of the portions ofthe carbon layer 12 and the inorganic pigment layer 13 formed on theresist layers 17. The hydraulic pressure used when blowing the watershould be set at a level slightly higher than in known fabricationprocesses wherein any inorganic pigment layer is not formed. By this, asshown in FIG. 3(C), a matrix pattern consisting of the carbon stripes12a and the inorganic pigment layers 13a formed thereon was formed withclear edges. The non-formed portions of the matrix pattern were windowportions 18.

As shown in FIG. 3(D), a red fluorescent stripe 14r, a green fluorescentstripe 14g and a blue fluorescent stripe 14b were formed in the windowportions 18 according to a known outside exposure method with eachstripe having a thickness of about 20 μm. Thus, the pigment layer 13 isapproximately 75% as thick as the fluorescent stripes 14r, 14g or 14b.The exposure was made from the outer side of the glass panel 11 throughthe matrix pattern as an optical mask, so that the respectivefluorescent stripes 14r, 14g and 14b did not extend over the uppersurface of the respective white pigment layers 13a, but were selectivelyformed on the window portions alone. For the formation of the respectivecolor fluorescent stripes, fluorescent slurries were applied and dried,followed by exposure to light and development with water. In thepractice of the invention, the adhesiveness of the fluorescent stripeswas improved and the drop-off failure of the fluorescent stripes at thetime of the development with water was reduced by about 20%.

Thereafter, as shown in FIG. 3(E), the inner surface of the panel wasentirely covered, for example, with an acrylic emulsion to form anintermediate film 15. The intermediate film 15 was formed by a two-layercoating method. The main purpose of the two-layer coating method was toimprove mirror surface properties of a metal backing through animprovement in the smoothness of the intermediate film, therebyimproving the brightness of the picture. In general, when a binder ofthe fluorescent layer having cationic properties and an acrylic emulsionhaving anionic properties are contacted, the acrylic ingredient willfail to properly disperse to cause an irregular coating of theintermediate film, which results in a deterioration of the mirrorsurface properties of the metal backing. To avoid this, a non-ionicacrylic emulsion (commercial name: Primal C-72, Rhom & Haars Inc.) wasused as a first layer (formed at the side of the fluorescent layer) andan anionic acrylic emulsion (commercial name: Primal C-72, Rhom & HaarsInc.) was used as a second layer. By this, the smoothness of theintermediate film 15 was improved and the discoloration was preventedfrom occurring as would conventionally take place since the pH wasshifted toward an acid side. This intermediate film 15 was formed on theinner surface of the panel with a reduced surface step and results in areduced irregularity in the film thickness.

The formation of the intermediate film 15 could be made, aside from theapplication of the acrylic emulsion, by applying water on the innersurface of the panel and developing a lacquer. In this case, theinorganic pigment layer 13a and the fluorescent stripes 14r, 14g and 14bshould preferably be formed substantially at the same height.

Subsequently, a metal backing film 16 is formed such as by vacuumdeposition of aluminum on the intermediate film 15.

Next, a thermal treatment was effected at a temperature of about 420° C.to remove the photosensitive resins from the intermediate film 15 andthe fluorescent stripes 14r, 14g and 14b with the respective colors bythermal decomposition. This step produces a panel with an inner surfaceprovided with the fluorescent stripes 14r, 14g and 14b and the inorganicpigment layers 13a covered with the metal backing film 16. In thisthermal treatment, since the intermediate film 15 was formedsubstantially in a uniform thickness and the metal backing film 16 wasformed with fine pinholes by the action of the projections on the uppersurface of the inorganic pigment 13a (see points 3a of FIGS. 1 or 2),aluminum lifting caused by generation of gases by thermal decompositionwas not observed.

The panel fabricated in this manner was assembled in a color cathode raytube according to an ordinary procedure to measure its luminance.Comparison with known color cathode ray tubes where any inorganicpigment layer 13a was not formed revealed that with a 20 inch sizecathode ray tubes, the luminances for the respective colors wereimproved by 10% to 15% and with 36 inch size cathode ray tubes,luminances of some cathode ray tubes were improved by 30%.

The reason why the luminance is improved when the present invention isapplied is that most of the side walls of the fluorescent stripes 14r,14g and 14b are contacted with the inorganic pigment layers 13a andluminous rays emitted from the fluorescent particles are reflected backinto the fluorescent particles by the inorganic pigment layer along withlight reflected at inclined portions of the metal backing film 16 beingreflected toward the upper surface of the inorganic pigment layers 13a.As a result, the amount of the luminous ray components absorbed directlyin the carbon stripes 12a becomes very small.

In the foregoing, the fabrication of the color cathode ray tubes of thestriped type has been described. Similar results are obtained when thepresent invention is applied to color cathode ray tubes of the dottedtype and monochromatic cathode ray tubes.

As will become apparent from the above, according to the method of theinvention for fabricating a cathode ray tube, improvements of theluminance through formation of a thick fluorescent layer, prevention ofthe fluorescent layer from coming off and prevention of aluminum liftingare achieved. Especially, with color cathode ray tubes, the colorimetricpurity can be improved in addition to the above advantages. Moreover,when white materials are used as the inorganic pigment, the luminouscomponent of fluorescent materials is effectively utilized with agreater advantage in attaining high luminance. The above step can bereadily incorporated in an existing fabrication line of cathode raytubes without needing much additional equipment costs and without areduction of productivity.

In the cathode ray tubes fabricated according to the invention, theallowance of beam landing is increased due to the presence of theinorganic pigment layer so that while a degree of freedom of design isincreased, the fineness can be readily attained.

Although various minor modifications may be suggested by those versed inthe art, it should be understood that we wish to embody within the scopeof the patent granted hereon all such modifications as reasonably andproperly come within the scope of our contribution to the art.

We claim:
 1. A method for fabricating a cathode ray tube of the typewhich includes a panel having a fluorescent pattern on an inner surfaceof the panel, the method comprising the steps of:selectively forming aresist layer corresponding to a fluorescent pattern on an inner surfaceof a panel of a cathode ray tube; applying a slurry of a light-absorbingmaterial on the entire inner surface of the panel including the resistlayer to form a light-absorbing layer; applying an inorganic pigmentslurry with an inorganic pigment powder dispersed therein over theentire light-absorbing layer to form a pigment layer having surfaceirregularities and a substantial thickness; selectively removing theresist layer and portions of the light-absorbing layer and the pigmentlayer provided on the resist layer by a reverse development to from alight-absorbing pattern having removed portions separated from eachother; and forming a fluorescent layer at least on the respectiveremoved portions of said light-absorbing pattern with the pigment layeracting as a partition wall for separating the fluorescent layer inadjacent removed portions.
 2. A method according to claim 1, whereinsaid light-absorbing pattern is carbon.
 3. A method according to claim1, wherein said pigment layer is made of a powder of a pigment selectedfrom a group consisting of C and MnO₂.
 4. A method according to claim 1,wherein said pigment layer is made of a powder of a white pigment.
 5. Amethod according to claim 4, wherein said white pigment is a memberselected from a group consisting of CaO, TiO₂, Al₂ O₃, MgO and ZnS.
 6. Amethod according to claim 1, wherein said powder has a size of notlarger than 1 μm.
 7. A method according to claim 1, wherein said pigmentslurry comprises the inorganic pigment powder, colloidal silica and purewater.
 8. A method according to claim 7, wherein said pigment slurryfurther comprises an acrylic emulsion as a dispersant.
 9. A methodaccording to claim 1, wherein said pigment slurry is sprayed over theentire light-absorbing layer.
 10. A method according to claim 1, whereinsaid pigment layer is formed in a thickness of a range of 10 to 20 timesgreater than the thickness of the light-absorbing layer.
 11. A methodaccording to claim 1, which includes applying an intermediate layer oftwo sub-layers on the fluorescent layer and the pigment layer of saidlight-absorbing pattern.
 12. A method according to claim 11, whichincludes forming a thin metal backing layer on the intermediate layerand then thermally decomposing the intermediate layer.
 13. A methodaccording to claim 1, wherein fluorescent layers of three primary colorsare formed at least on the removed portions so that the three primarycolors are arranged side-by-side in the fluorescent pattern whereby acolor cathode ray tube is obtained.
 14. A method according to claim 1,wherein the step of applying an inorganic pigment slurry sprays theslurry onto the light-absorbing layer.
 15. A method for fabricating acathode ray tube of a type which includes a panel having a fluorescentpattern on an inner surface of the panel, the method comprising thesteps of:selectively forming a resist layer corresponding to afluorescent pattern on an inner surface of a panel of a cathode raytube; applying a slurry of a light-absorbing material on the entireinner surface of the panel including the resist layer to form alight-absorbing layer; applying an inorganic pigment slurry with aninorganic pigment powder dispersed therein over the entirelight-absorbing layer to form a pigment layer having surfaceirregularities; selectively removing the resist layer and portions ofthe light-absorbing layer and the pigment layer provided on the resistlayer by a reverse development to form a light-absorbing pattern withwindow portions; forming a fluorescent layer at least on the respectivewindow portions of the light-absorbing pattern; applying anintermedialayers of said light-absont layer and the pigment layers ofsaid light-absorbing pattern; forming a thin metal backing layer on saidintermediate layer; and subsequently thermally decomposing theintermediate layer.
 16. A method according to claim 15, wherein saidstep of applying an inorganic pigment slurry provides an inorganicpigment slurry having a powder selected from a group consisting of C andMnO₂.
 17. A method according to claim 15, wherein the pigment layer ismade up of a powder of a white pigment.
 18. A method according to claim17, wherein the white pigment is selected from a group consisting ofCaO, TiO₂, Al₂ O₃, MgO and ZnS.
 19. A method according to claim 15,wherein said pigment layer is formed in a thickness of about 75% of thethickness of the fluorescent layer and acts as a partition wall toprevent light from passing between fluorescent layers in adjacent windowportions.
 20. A method according to claim 15, wherein the step ofapplying the inorganic pigment slurry sprays the slurry over the entirelight-absorbing layer.